In recent years, mobile telephone sets have been experiencing size reduction of casings and high-density mounting of devices, as well as significant improvements in multifunctionality by including a video phone function and providing a waterproof property to the casings, and in performance by increasing definition and image quality of installed devices such as a camera and a display.
Along with the improvements in multifunctionality and performance, a central processing unit (CPU), which is one of the installed devices of the mobile telephone set, is required to process a larger amount of data at higher speed. In particular, a large amount of data needs to be processed at high speed in reproducing high definition (HD) video and making video phone call, and hence power consumption of the CPU is very large.
While the power consumption of the CPU is being increased, there is a situation in which it is difficult for the casing of the mobile telephone set to radiate heat generated inside the casing due to the above-mentioned size reduction, high-density mounting, and provision of the waterproof property to the casing. Therefore, mobile telephone sets in recent years tend to generate a large amount of heat.
The heat generated by the mobile telephone set may not only damage the equipment and its devices, but also cause a burn of a user or a fire accident. Therefore, as represented by the Product Liability (PL) Act, measures against the heat generated by the mobile telephone set are one of important factors of product quality.
Technologies relating to reduction in power consumption of, and measures against the heat generated by, the mobile telephone set are disclosed in, for example, Patent Literature 1 (Japanese Unexamined Patent Application Publication (JP-A) No. 2002-27145) and Patent Literature 2 (Japanese Unexamined Patent Application Publication (JP-A) No. 2007-312139).
Patent Literature 1 discloses a mobile telephone set having a video phone function which, in order to reduce power consumption, is configured to stop, during a video phone call, decoding processing on a received video signal and/or encoding processing on a video signal to be transmitted in response to an operation of a user, and display and/or transmit to a communication partner an alternative image (still image). Patent Literature 1 also describes that heat generated by the mobile telephone set is suppressed by stopping the decoding processing and/or the encoding processing on the video signal when unnecessary.
Patent Literature 2 discloses a mobile telephone set having a video phone function which, in order to suppress an increase in temperature at a surface of a casing, is configured to, during a video phone operation, after a temperature signal from a temperature sensor for detecting a temperature near the mobile telephone set has exceeded a first threshold and further a grace period has elapsed, suspend a photographing operation of a camera and transmit an alternative image (still image) to an opposite side, and when the temperature signal falls to or below a second threshold, which is lower than the first threshold, return to the normal video phone operation.
However, in the technology disclosed in Patent Literature 1, the user judges whether or not to stop the decoding processing and/or the encoding processing on the video signal, and hence an operation closely associated with the situation of heat generation of the mobile telephone set is impossible. Further, when the decoding processing and/or the encoding processing on the video signal is stopped, the video of the video phone call that has been displayed is suddenly interrupted by the alternative image, which has been prepared in advance and is different from the situation during the video phone call, and hence the user and the communication partner feel uncomfortable.
Also in the technology disclosed in Patent Literature 2, when the photographing operation of the camera is suspended, the video of the video phone call that has been displayed is suddenly interrupted by the alternative image, which has been prepared in advance and is different from the situation during the video phone call, and hence the communication partner feels uncomfortable.